A number of politicians, particularly many Republicans, are questioning whether global warming is being caused by human activity. Some are now claiming that scientists are split on the issue. Politifact decided to check up on these ridiculous claims:

To begin with, a 2007 report from the U.N. Intergovernmental Panel on Climate Change, the world’s leading international scientific body on climate science, states: “Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations. The observed widespread warming of the atmosphere and ocean, together with ice mass loss, support the conclusion that it is extremely unlikely that global climate change of the past 50 years can be explained without external forcing, and very likely that it is not due to known natural causes alone.” (External forcing refers to anything that changes the climate that is outside of the normal climate system.)

A 2009 report from the U.S. Global Change Research Programreached a similar conclusion: “Observations show that warming of the climate is unequivocal. The global warming observed over the past 50 years is due primarily to human-induced emissions of heat-trapping gases. These emissions come mainly from the burning of fossil fuels (coal, oil, and gas), with important contributions from the clearing of forests, agricultural practices, and other activities.”

Current climate change research was reviewed again this year by the National Research Council and the National Academy of Sciences. The committee it assembled concluded that global warming poses significant risksand is happening primarily because of greenhouse gas emissions from human activities. It rejected the idea that those findings are in any way questionable.

“Although the scientific process is always open to new ideas and results, the fundamental causes and consequences of climate change have been established by many years of scientific research, are supported by many different lines of evidence, and have stood firm in the face of careful examination, repeated testing, and the rigorous evaluation of alternative theories and explanations,” the committee’s report said.